function minimum = get_min_raster(img, i, j)
    if j==1 || i==1
        topleft = intmax;
    else
        topleft = img(i-1, j-1);
    end
    if i==1
        top = intmax;
    else
        top = img(i-1, j);
    end
    if j==1
        left = intmax;
    else
        left = img(i, j-1);
    end
    if j == size(img, 2) || i == 1
        topright = intmax;
    else
        topright = img(i-1, j+1);
    end
    minimum = min([topleft, top, left, topright]);
end